A ball valve is a valve that opens and closes by rotation of a ball. The ball has a port therethrough such that when the port is in line with ends of the valve, flow will occur. The ball sits in, and is sealed by, valve seats.
As is well known, a main requirement in the manufacture of ball valves is that an effective seal be maintained between the valve seats and the ball at all times. Many and varied forms of annular seats have been devised for this purpose.
One ball valve seat arrangement is described in U.S. Pat. No. 3,384,341 to Ripert (“Ripert”). A main feature of that arrangement resides in the cross-sectional shape of the seats (or “sealing rings”) that is formed to have a somewhat arcuate overall formation with a substantially concave outer surface and a substantially convex inner surface. When pressure is applied to the inner surface, by contact with the ball, it tends to flex inwardly and due to the concavity of the outer surface, the middle portion of the ring increases in circumference under tension. By way of background, the valve of Ripert will be described in further detail with reference to FIGS. 1 to 3 herein. With particular reference to FIG. 1 of Ripert, a portion of a typical ball valve construction is shown as comprising a two piece valve body 10, having a main portion 12 including a tapped bonnet portion 14 receiving a valve spindle 16. The main body 10 is recessed axially to provide a fluid inlet 18 and an enlargement 20 constituting a valve chamber 21. The outer end of the enlargement 20 is tapped to threadably receive the minor portion of the valve body 22, which is also recessed axially to provide a fluid inlet 24. The inner ends of the fluid inlets 18 and 24 are each provided with sealing ring accommodating grooves 30 into which is adapted to fit sealing ring 32. The terminal end 17 of the spindle 16 is shaped in rectangular form to fit loosely with a corresponding slot 33 and a ball 34. Rotation of the spindle 16 causes a corresponding rotation of the ball 34, which includes an axial recess 35, between open and closed positions relative to the fluid inlets 18 and 24 with the sealing rings 32 acting to maintain the seal between the outer spherical surface of the ball and opposed portions of the valve body surrounding the fluid passages. FIG. 2 shows a sealing ring in perspective and partially broken view of Ripert, in which concave outer surface 50 and convex surface 52 are identified. In operation, and assuming that the spacing between the opposed ring accommodating grooves 30 is such that a minimum deflection only of the sealing rings 32 as shown in FIG. 3 is necessary, the outer surface of the ball 34 (FIG. 1) bears against the apex 57 of the inner surface of the ring so that it is urged inwardly along the centre as indicated by the arrow A. The deflection of the ring 32 in the direction A, due to the concave outer surface 50, places the ring under tension causing it to bear against the ring accommodating groove 30 along the direction of the arrows B and C bringing the surfaces 51 and 54 more tightly against the groove surfaces 61 and 63. At the same time, a convex inner surface is altered, as indicated at D, conforming to the curvature of the ball 34. The preferred minimum deflection illustrated in FIG. 3 will give the desired maximum sealing effect with the minimum of friction contact with the ball 34 making for ease in valve adjustment but the same maximum sealing effect is obtained with a condition of maximum deflection of the sealing ring, as shown in FIG. 3, without seriously affecting the friction resistance by the contact of the sealing rings with the ball 34. In effect, any deflection of the sealing rings by the ball outer surface bearing on the inner surface 51 of the ring increases the circumference while placing the ring under tension giving the desired sealing effect in the directions B and C. In other words, when the ball 34 abuts the convex surface 52, it will stretch or expand the circumference of the convex surface 52 thus placing it under tension. The spacing of the concave surface 50 from the connecting surface or inclined surface wall 65 of the groove 30 allows the ring to be placed under tension on bearing of the surface 52 by the ball 34. The sealing ring may also be in an alternative form by having a smooth arcuated inner surface rather than a surface with an apex. The same principles of deflection apply.
Due to the temperature and load conditions under which the sealing ring (or “seat ring”) is required to operate, deformation can be a substantial problem result in shortened lifespan. Several attempts have been made to engineer sealing rings which are resistant to deformation.
U.S. Pat. No. 3,486,733 to Gorden et al. (“Gordon”) discloses, according to the abstract, a seat ring for ball valves where the seat ring includes a core made of a resilient material and encapsulated by a molded body. The molded body may be made of rubber, rigid material such as ceramic or graphite, or synthetic plastic materials. The resilient core proved in Gorden enables the seat ring to withstand higher load. In one embodiment, there are two sections of the encapsulated core: “section 30 is made of resilient material and acts as spring. Section 31 may be made of rigid, non-resilient material” (see col 3, lines 37-38). Finally, the Gorden patent states that “the metal core provides the principle bending resistance . . . [and] insures full recovery of the seat [ring] as a whole to its normal shape when pressure is relieved so that no permanent deformation occurs” (see col. 4, lines 44-45 and 52-54). The resilient cores disclosed by Gorden are generally T- or V-shaped.
U.S. Pat. No. 4,113,231 to Halpine (“Halpine”) teaches, according to the abstract, a seat ring comprising flexible elastomeric material (see col. 2, line 46) such as a helical spring 46 which is wound of suitable steel spring wire and which is of a diameter and length such that it may be fitted into the circular cavity 48 of the seat ring and held in place by the shape of the ring (see col. 2, lines 59-62). When the assembly is fully assembled, there is sufficient pressure at the seal 50 against the ball surface 19 so that the spring is slightly distorted, thus providing an outward force against the surface 19, sufficient to provide sealing pressure against the fluid pressure (see col. 3, lines 4-8).
U.S. Pat. No. 4,071,220 to lino (“lino”) teaches, according to the abstract, that a “seal member 15 includes an annular groove or recess 85 in which the expansively resilient member 18 is forcibly engaged. The expansively resilient member 18 is spirally wound around itself” (see col. 6, lines 29-32) and “the groove width of the annular groove 85 formed in the seal member 15 is slightly smaller than the spiral diameter of the member 18. Accordingly, the annular resilient member 18 is forcibly engaged into the annular groove 85 [such that member 18] has its cross-section slightly flattened to a somewhat non-circular cross-sectional configuration (see col. 6, lines 48-55). The pressure required to contact body 14 with seal member 15 is provided by the annular expansive resilient member 18, which also compensates for damage and deformation of the seal member 15 as it is worn down (see col. 7, line 50 to col. 8, line 15).
Springs, including coiled springs (or helical springs) disclosed in the Halpine and lino patents suffer from known problems over time, including degradation, loss of tempering, and sagging.